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NFS max rsize on Solaris – gotcha

When mounting NFS file systems there is an option to set the max rsize requested. For example:

mount -o rsize=1048576,wsize=1048576,proto=tcp,vers=3 /foo

The general rsize used is 32K,  for example in Oracle documentation, but for large sequential I/O the larger rsize can make a big difference. In some tests the larger rsize was twice as fast.

Unfortunately though, if the client is Solaris the larger rsize is ignored because of a kernel parameter. That parameter is nfs3_bsize which defaults to 32K and limits the rsize. To change the value either add it to /etc/system for use on reboot or for changing it immediately, use mdb:

mdb -kw
> nfs3_bsize/D
nfs3_bsize:     32768
> nfs3_bsize/W 100000
nfs3_bsize:     0xd             =       0x100000